Senior cat recovering from abcess?

My cat is recovering from an abscess. I took him to the vet 2 days ago, and they erupted most of it, but not all. It isn't pussing anymore, but when he got the abcess he lost all of the fur in the area. Now the scab is turning a very dark red. He's started eating more regularly, but he still isn't back to himself. Does anyone have any ideas of what I can do to make him more comfortable? I think I will be taking him to another vet for a different opinion if he isn feeling better soon. He sleeps a lot, and he gets the shakes quite often. He's 13 years old.
Thanks so much for your help.
I can post pictures of the abscess, but I'd rather not because it isn't very pretty.

Did they give him antibiotics too?  Why didn't they erupt it all, did they say?  Did they tell you to put warm compresses on it to draw the rest out?  Obviously is it's scabbing over now, it's too late to do that now. 

If he's eating now, I take that as a good sign!  As far as "the shakes", do you mean he is unsteady on his feet, or he is shivering?  If he is shivering, it could mean he is running a fever, or his body temp is actually too low, or it could be something else...even hypoglycemia.  Does he feel hot or cold?  If it IS shivering and he is doing this pretty consistently, I think a follow-up visit is needed, especially having an abscess that wasn't fully cleaned out.  Is he showing any other symptoms of anything...vomiting, diarrhea?  I think sleeping a lot, especially at his age, is probably pretty common this soon after an abscess, simply because the body needs rest in order to heal, but I could be wrong

They couldn't get all of it out because he's rather feisty, which is another reason that I couldn't do a compress. He bites and scratches. I was hoping they could put him under so they could erupt it, but they didn't and I'm not sure why.

He's on an antibiotic for the next week or so. The vet said it should take care of the abscess.

He doesn't totally shiver, he just twitches a lot. He sometimes shivers but not completely constantly. I'll watch more closely and update soon.

He did vomit before, but it was because of all of the hair he swallowed. He lost complete fur in an area about 2x2 inches. Since then to my knowledge he hasn't vomited but he's an outdoor/indoor cat so I'm not really sure. Same with diarrhea.

Is it possible to keep him inside while he's recovering?  It's really the only way you'll be able to tell what's happening with him...whether or not he's vomiting, has diarrhea, etc.  Plus, you need to make sure he get's his daily antibiotic, so you need to make sure he's home .  AND, if any of the wound is still open, it could get re-injured more easily if he's outside (I would think). 

I'm still not sure I grasp this twitching, shakes thing...sorry

2 X 2 inch bald spot at the abscess.  Gosh, pretty big abscess, huh?  What caused it, do you know?  Is that area inflamed?  Can you touch it without him going ballistic?

more

My senior 12 year old just went through the exact same thing except he had surgery and they put a drain in. I don't know if that's any better then just letting it drain after it erupts, the surgery incision is huge! Cats will lose all the hair around the drainage site, and mine get those 'twitches' too, they just take off running after biting at a spot. It may be nerves, As for the shivering I really wondered if it wasn't from pain, he seemed to stop when I stroked and calmed him. An outside cat recieved a bite on one of her back legs and lost all the hair on her rear end. I felt so sorry for her, but she was a feral and another one too smart for the traps. I do give them antibiotics when I feed them at these times and somehow they pull through.

I do try to keep him inside but he actually prefers the outdoors! He sleeps with my dog in the garage and comes in for food and occasionally sleeps in here, but he doesn't like people at all (especially kids, and there's no shortage of children here) and I've tried keeping him in my room but I can tell he's more comfortable out there.

I have no idea what caused the abscess, someone saw a feral cat around here and they could've been in a fight, but I never saw any evidence and since my cat keeps to himself most of the time I didn't notice the abscess until at least 24 hours after it happened, and I'm pretty sure he lost all of the fur in a day (he coughed up the biggest hairball I've ever seen) and I think he is still losing it around the wound, but not as fast.

I can touch it, but he doesn't particularly enjoy it. Just the very tips of my fingers. He's still on the antibiotics and I haven't missed a day since I got them. He lost the shakes now, but the abscess turned a really mad red-really really deep red, and it looks like he's less comfortable than he was a few days ago.

Do you think I should go back for a second opinion or wait a few days and go from there?

By the way, thank you all SO very much for your help. I appreciate it so much. I have no cat owner friends nearby

If the area is really deep red, that doesn't sound good to me.  Can you tell if it's hot to the touch?  On a human, if it were red and hot to the touch, I would be on my way to the dr, as that would indicate infection.  But he's on an antibiotic already, so, to me, that's kind of curious.   Well, I'd at least CALL the Vet (the one that treated him already) and mention it.  Is he still eating ok?

Good news guys, he's fully recovered. The hair is growing back, and he's eating an drinking again and stopped shaking! If someone wants to see before and after pictures let me know

I'm so glad he's recovered